1. Field of the Invention
The present invention relates to a solid state image sensor.
2. Description of the Prior Art
In some cases, solid state image sensors are sold to their users without being assembled with any other device, the sales called the "chip sales". In such a case, the solid state image sensor requires much care when it is handled because it has light receiving portions very sensitive to dirt. However, in practically handling a solid state image sensor by the chip, the light receiving portions are highly possibly contaminated by dust or in a certain gaseous environment. For the above reason, there must be a process of cleaning the light receiving portions in the stage of assembling the solid state image sensor. The simpler the cleaning process is, the more advantages in cost will result. Therefore, in the case of a simplest process, the light receiving portion has been merely wiped with a cotton swab or the like impregnated with organic solvent.
When the light receiving portions are wiped with a cotton swab or the like impregnated with organic solvent in the cleaning process, since minute projections and recesses on the order of microns are formed on micro lenses 11 provided on the surface of the solid state image sensor as shown in FIG. 5 which illustrates a sectional view of the solid state image sensor provided with the micro lenses, dust or the like has been forced into recesses 16 formed between micro lenses 11, which has conversely 10 resulted in aggravating the contamination of the solid state image sensor.
Furthermore, there is a high possibility of applying a great stress onto the surface of the solid state image sensor when cleaning the solid state image sensor with a cotton swab or the like. Therefore, in the case of the conventional solid state image sensor, it is highly possible to damage the micro lenses 11 which are relatively soft.
Even in the case of a solid state image sensor which is not provided with the micro lens 11, a surface of the solid state image sensor is formed of silicon oxide or silicon nitride having a relatively high surface energy, and therefore the dust once attached to the surface is hardly removed.
In FIG. 5, there are shown a semiconductor substrate 1, light receiving portions 2, charge transfer electrodes 3 for transferring electric charges generated at the light receiving portions 2, electric charge transfer portions 4, a layer insulating film 5, a light shutting off film i.e. shielding film 6, a transparent flattening film 7 suppressing a difference in level between the light receiving portions 2 and the charge transfer electrode 3 below a specified value and made of a resin material or the like having a high optical transmittance, a first color filter 8a, a second color filter 8b, a third color filter 8c, and a first transparent protection layer 9 for protecting the surfaces of the first color filter 8a, second color filter 8b, and third color filter 8c, reducing the differences in level between the filters, and assuring appropriate focal lengths of the micro lenses 11.